SPECIATION OF METALS IN YAMUNA RIVER SEDIMENTS

The chemical forms of cadmium, copper, lead and zinc have been determi ned using the fractionation scheme of Tessier et al. in the bed sedime nts of River Yamuna. Sediment characteristics do not show any signific ant variations except that carbonate content is consistently higher in the post-monsoon season. Silicon and aluminium are the most abundant elements followed by K, Na, Ca, Fe, Mg and Mn in that order, the essen tial minerals being quartz and biotite. The speciation profiles for a particular metal show a similar trend throughout the stretch with no s ignificant spatial variations. Cadmium is mostly associated with carbo nate content and thus has a possibility of becoming readily bioavailab le. Major fraction of copper is bound to organic matter while that of zinc to Fe-Mn oxide. Thus they cannot be easily leached out and may po se less environmental risk. Major percentage of lead is found in the F e-Mn oxide fraction; moderate contributions being made by carbonate an d residual fractions. The total lead in the sediments is higher, there fore even a small fraction of lead bound to carbonate content can pose problems to the ecosystem. There are good correlations between the di fferent constituents and the major metal fractions associated with it.